The yes vote was strongest for the first group, with the panel voting 19-3. For the second group, the panel voted 19-2 with 1 abstention. For the third group, the panel voted 12-8 with 2 abstentions.

The FDA does not have to follow the advice of the advisory panel, but it typically does. A final decision is expected by June 15. Truvada is already used ''off-label" as a preventive drug in high-risk people, such as men who have sex with men.

AIDS activists and doctors have been sharply divided about what FDA approval for healthy people will mean. In some studies, the drug reduced the risk of infection by 75%.

Critics of the decision say an HIV-preventive drug will send the wrong message, leading to the decline of condom use.

Advocates say a preventive drug will be a welcome addition to other measures to reduce the AIDS epidemic. "It's not a panacea, not a blanket answer, but it is one more piece of the prevention puzzle," says William McColl, political director of AIDS United.

The cost of the drug is about $1,100 a month, says Patrick O'Brien of Gilead Sciences, its maker. With insurance, the cost is often a $10 co-pay, he says.

About 1.2 million Americans have HIV, according to the CDC, although 1 in 5 is unaware. About 50,000 people in the U.S. each year are newly infected.

More About Truvada

Truvada contains two medicines, Emtriva and Viread. They are combined in one pill. For the treatment of HIV, Truvada is used in combination with other HIV medicines.

The drug works by helping to block a chemical in the body needed for HIV to multiply.

As the advisory committee listened to evidence about the drug, some expressed concerns that people would share the medication. Others wondered if approval for healthy persons would result in a decline in safer sex practices such as condom use.

If people who took the medication got infected anyway, some worried that drug-resistant strains might develop.

Other questions addressed by the expert panel, such as whether to require doctors who prescribe it to receive education about the drug, were not voted on. Nor was the question about how often those who take the preventive drug would get
HIV testing.

Truvada as Preventive: Advocates

"It's pretty clear from clinical data and a number of clinical trials that there really is a protective effect from Truvada," says McColl of AIDS United. "Our organization does support the use of Truvada for HIV prevention."

"We don't send people to places where malaria is present and say, 'You can only have netting or the [anti-malarial] vaccine,'" he says.

Truvada as Preventive: Critics

Approving an HIV preventive drug is not productive and may backfire, says Michael Weinstein, president of AIDS Healthcare Foundation.

"We're opposed to the FDA indication for prevention of HIV [with Truvada]," he tells WebMD.

The data do not support its value as a preventive, he says. He worries, too, that the drug may give people at risk a false sense of security.

"If people think they are protected they won't use condoms, and the rate of infection will actually increase," he says.

Truvada as Preventive: Limited Role

Rodney Wright, MD, director of HIV programs in the department of obstetrics and gynecology at Montefiore Medical Center in New York, sees a limited preventive role for the drug.

"I'm not in favor of widespread use of it as a preventive because of concerns over adherence," he says. "We know it does not work if it is not taken every day."

He does see a role, he says, for the HIV-negative partner of a couple trying to conceive. If the HIV-negative partner would take the drug as a preventive, it could help them have a safer pregnancy and not pass the infection to the baby, Wright tells WebMD.

Truvada: The Research

Gilead presented numerous study results to the advisory panel.

In one study of nearly 2,500 high risk HIV-negative men who had sex with men, the risk of getting HIV was reduced by 44% in those who took Truvada compared to those who took placebo.

Among the men in the study (known as iPrEx), those who took the drug at least 90% of the time reduced their risk of getting HIV up to 73% compared to placebo.

In the Partners PrEP Study, including 4,747 couples in which one partner was HIV-positive, those who took the pill daily had a 75% lower risk of getting infected compared with those who took placebo.

However, a study conducted in women by Family Health International was stopped in April 2011. After enrolling nearly 2,000 women, it did not find the daily dose effective in preventing infection in HIV-negative women.